To date the problems of enhanced scan volume and increased readability of bar codes held at different orientations to a scanner have only been addressed by the use of dual aperture scanners.
Commonly assigned U.S. Pat. Nos. 5,229,588, 5,684,289, and 5,886,336 disclose a typical dual aperture optical scanner. The scanning light beams from a laser diode pass through substantially horizontal and vertical apertures to provide more item coverage than a single aperture scanner.
Known multi-aperture optical scanners produce scan patterns with gaps in item coverage. These gaps increase as the item is moved away from an ideal position in the center of the scan volume.
Therefore, it would be desirable to provide an optical scanner which is not only capable of reading a bar code label at different orientations to the scanner, but at different distances to the window.
Scanning bar codes which are located at different distances to the scanner, especially small bar codes such as the new RSS symbology, is extremely difficult. The problem is exacerbated by the characteristic of present day bar code readers that the focal length of the scan light can vary as it traverses the scanner. This is due to the extremely complex network of pattern mirrors utilized in scanners, which can result in different optical path lengths and therefore different focal positions for light passing through the scanner at different times.
The complexity of, especially dual aperture, scanners will be described in order to illustrate another advantage of the present invention, which is the simplicity and corresponding ease of construction of the scanner, which helps mitigate the problems detailed above.
As will be illustrated in more detail below, with reference to FIGS. 1 to 6, present day scanners comprise, a laser assembly, spinner assembly, collection optics, pattern mirrors, detector assembly, electronics, a window and scanner housing which contains all the individual assemblies. In operation, the laser beam intercepts the polygon spinner and is subsequently scanned in a single axis towards a set of pattern mirrors which reflect the individual scan lines out the window and onto a barcode. The laser energy is then reflected off of the barcode and a portion is gathered by the collection optics and focused onto the detector generating a signal to be decoded by the electronics. The positions at which the scan lines exit the window are static, and are contained in a relatively small portion of the hemispherical volume available outside and adjacent to the window (FIG. 6). Consequently, the readability of barcodes is limited to certain positions within that small scan volume